Caption: Somatotropin. Computer model of a molecule of the human growth hormone (hGH) somatotropin (or somatotrophin). The atoms (tubes) of this large molecule are colour-coded: carbon (green), sulphur (yellow), nitrogen (blue), hydrogen (grey) and oxygen (red). This hormone is a protein, and is made up of 191 amino acids and has a molecular weight of 21,864. It is secreted from the anterior part of the pituitary gland. It plays a vital role in the normal growth of a human. It is also used to retard the effects of ageing, though a possible side-effect is an increased risk of cancer. It is also abused as a drug by athletes wanting to build muscle and improve sporting performances.